Photovoltaic cells are often used to recharge batteries, or to provide power to an electric grid and/or a building through an inverter. Photovoltaic cells often, however, provide less output power than expected from known device efficiency and illumination.
One reason that photovoltaic cells may deliver less than optimum power is that their maximum power output under typical conditions is often at a voltage that is not well matched to their load. This mismatch occurs, in part, because typical photovoltaic cells are temperature sensitive, and a sufficient quantity of photovoltaic cells must be connected in series to provide required voltage magnitude at high temperatures. This large photovoltaic cell count becomes excessive at low temperatures where photovoltaic cells' maximum power output voltage is highest. Similarly, maximum power output voltage may change with illumination changes. Other losses occur when any one series-connected photovoltaic cell in a module of interconnected photovoltaic cells (“photovoltaic module”) generates less current than other photovoltaic cells in the photovoltaic module. Barring additional circuitry, the output current of a series string of photovoltaic cells is effectively limited by photocurrent produced in the weakest, or most shaded, cell.
Since shading affects photocurrent produced in photovoltaic cells, often limiting current production of a series string of cells to that of a most-shaded cell of the string, un-shaded cells in the same series string may yield substantially less power than they are otherwise capable of. Further, shading of cells may vary with time of day, sun angle, obstruction position, and even the position of wind-blown leaves or other debris on a photovoltaic panel.
Maximum Power Point Tracking (MPPT) controllers are frequently connected between a photovoltaic module and a load, such as an inverter or a battery. MPPT controllers typically include a switching circuit, such as a buck DC-to-DC converter, that converts an input power at a module voltage to an output power for the load at a load voltage, and control circuitry that seeks to find a module voltage at which the photovoltaic module produces maximum power. The switching circuit of the MPPT controller serves to decouple the photovoltaic module and load voltages. Some examples of MPPT controllers and associated systems and methods are discussed in U.S. Patent Application Publication Nos. 2012/0043818, 2012/0043823, and 2012/0044014 to Stratakos et al., which are incorporated herein by reference.
Many photovoltaic system applications require communication between system components. For example, safety requirements may necessitate that MPPT controllers be capable of being remotely disabled. As another example, MPPT controllers may need to communicate status information to a central device for photovoltaic system monitoring. Accordingly, conventional MPPT controllers are frequently capable of communicating with a remote device using radio frequency (“RF”) networking or power line communication (“PLC”) networking. Both RF and PLC networking systems transmit data by generating a high frequency carrier wave, modulating the carrier wave, transmitting the carrier wave over a medium, and demodulating the carrier wave. Consequentially, RF and PLC networking systems require high frequency transceivers, as well as modulating and demodulating equipment. The transmission medium in RF networking systems is typically air, while the transmission medium in PLC networking systems is a power line. It is important to note that PLC networking operates on top of power delivery and distribution across a power line, and PLC networking typically does not disturb power delivery through the power line.